P4HB and colitis: In mice, genetic deletion of molecules involved in the UPR, such as IRE1β, the transactivator of UPR's Xbp1 (X-box binding protein 1) and Agr2 (Anterior gradient 2) target genes, which is a member of the ER protein disulfide isomerase (PDI) gene family are associated with either spontaneous intestinal inflammation and/or increased sensitivity to the experimental induction of colitis [125–127].